The solution will allow whatever you as the developer allow. If you only want to perform one call at a time, then you will need to use a mechanism to prevent multiple calls. Without knowing your solution, it is hard to say which is the best method to perform this. There are several ways - using a Lock, tracking using a variable, if all calls come from a single button click staying synchronous could help. Really, what you are asking is a design decision that you will need to incorporate into your solution.